1. Field of the Invention
The present invention relates to a process of forming an electrode for a chip-like electronic part and a holder for a chip-like electronic part, particularly to a process of forming an electrode comprising a conductive paste on an outer surface of a chip-like electronic part and a holder for a chip-like electronic part preferably used in carrying out the process.
2. Description of Related Art
FIG. 18 shows a perspective view of a chip-like electronic part 1, particularly a three terminal capacitor. End electrodes 2 and 3 are formed on respective end portions of the chip-like electronic part 1 and central electrodes 4 are formed at the central portion thereof.
Although not illustrated, first and second groups of inner electrodes are arranged alternately inside the chip-like electronic part 1 with the inner electrodes of the first group extending to the end electrodes 2 and 3 and the inner electrodes of the second group extending to the central electrodes 4. Accordingly, electrostatic capacitances formed between the inner electrodes of the first group and the inner electrodes of the second group can be taken out between the end electrode 2 or 3 and the central electrodes 4. The chip-like electronic part 1 is used to, for example, remove noise on a signal line by coupling the end electrodes 2 and 3 to the signal line and grounding the central electrodes 4.
As shown in FIG. 18, the central electrodes 4 extend across two opposing side faces of the chip-like electronic part 1. Because of limitations associated with the process commonly used to make the chip-like electronic part 1, the central electrodes 4 extend only partially on the other side faces of the chip-like electronic part. As a result, the central electrodes 4 do not extend entirely around the outer side surfaces of the chip-like electronic part 1.
The process for applying the central electrodes 4 is best understood with reference to FIG. 19. As shown herein, a groove 6 is provided in a paste base 5 which comprises an elastic body. The groove 6 is filled with a conductive paste 7 to form an elongated streak 8 of conductive paste 3. The chip-like electronic part 1 is held by a holder 9 so that one face of the chip-like electronic part 1 faces the streak 8 of conductive paste.
As best seen in FIG. 18, the chip-like electronic part 1 is an elongated parallel-piped structure having a main axis extending from end electrode 2 to end electrode 3. The central portion of the chip-like electronic part 1 is aligned with the streak 8 of conductive paste with the axis of the streak extending perpendicular to the central axis of the chip-like electronic part 1. The chip-like electronic part 1 is brought into contact with the paste base 5 and pressed against the paste base 5 to deform it and cause the conductive paste 7 to be applied to the outer surface of the chip-like electronic part 1 as shown by an imaginary line in FIG. 19. Although the conductive paste 7 extends across the entire side face of the chip-like electronic part 1 which faces the base 5, it only extends partway up the adjacent side faces of the chip-like electronic part 1.
The orientation of the chip-like electronic part 1 is then reversed so that its opposite face extends away from the holder and towards the paste base 5 and the process is repeated to place the conductive paste 7 on the opposite face (and particularly up the adjacent side faces) of the chip-like electronic part 1. Thereafter, the so applied central electrodes 4 are cured.
Instead of placing the conductive paste 7 in a groove 6 provided in the elastic paste base 5, the conductive paste may be applied (by printing or the like) on a flat face of a paste base 5 which can be either elastic or rigid. As another alternative, a reservoir of conductive paste located on one side of a slit plate can be extruded to the other side of the slit plate via the slit in the plate by applying pressure to the conductive paste.
The end electrodes 2 and 3 are formed by dipping the ends of the chip-like electronic part 1 into a tank of conductive paste.
As mentioned above, the central electrode 4 does not normally extend around the entire outer surface of the chip-like electronic part 1. However, it is preferable that it does to reduce unnecessary inductance components where the central electrode is used as a ground electrode.
It is not impossible to form the central electrode to extend around the entire circumference of the chip-like electronic part 1 using the process shown in FIG. 19. This result can be achieved by providing a sufficient amount of conductive paste to extend at least half way up the two side faces of the chip-like electronic part 1, for example, by making the groove deeper or pressing the chip-like electronic part 1 more strongly against the paste base 5. However, as shown in the sectional view of FIG. 20, overlap portions 12 are formed on flat end faces of the chip-like electronic part. These overlap portions 12 can hamper the mountability of the chip-like electronic part. Accordingly, it is preferable that a built-up portion, such as the overlap portion 12, not be formed at the central portion of any of the side faces of the chip-like electronic part 1.
This can be avoided by using a small enough amount of conductive paste that only one side of the chip-like electronic part receives the paste during any single application. However, this will necessitate four separate applications of the conductive paste which is not efficient.
It is an object of the present invention to provide a process of forming an electrode of a chip-like electronic part and a holder for a chip-like electronic part used in the process which can resolve the above described problem.
To this end, the process of the present invention forms an electrode on a chip-like electronic part of the type having a central axis, a polygonal cross section as viewed in a plane which is perpendicular to the central axis, a plurality of side surfaces extending in respective planes which are generally parallel to the central axis, and a pair of end surfaces extending generally parallel to the central axis, each adjacent pair of side surfaces meeting along a respective edge of the chip-like electronic part, the process comprising the steps of:
applying a first band of conductive material to at least one of the side surfaces; and
applying a second band of conductive material to the remaining side surface(s) in such a manner that the first and second bands meet at respective ones of the edges and together form a continuous band of conductive material extending around the outer periphery of the chip-type electronic part.
In the preferred embodiment, the first and second bands are applied to the side surfaces at an area that lies between the end surfaces, and more preferably in the middle, of the chip-like electronic part and do not extend to either end surface.
In the preferred embodiment, the chip-like electronic part has four side surfaces, the first band is applied to first and second contiguous side surfaces and the second band is applied to third and fourth contiguous side surfaces by bringing the side surfaces into contact with strips of conductive paste. The chip-like electronic part is first held in a holder with the first and second side surfaces extending outwardly from the holder and the first band is applied to the first and second side surfaces by moving a strip of conductive paste located on an elastic paste base into contact with the first and second side surfaces. Thereafter, the orientation of the chip-like electronic part is changed by either moving it within the same holder or moving it to a second holder to ensure that the third and fourth side surfaces extend outwardly from the holder. Once in this position, the second band is applied to the third and fourth side surfaces by moving a strip of conductive paste located on an elastic paste base into contact with the third and fourth side surfaces.
When desired, the first and second bands can be applied to the side surfaces at an area of the side surfaces located adjacent one of the end surfaces thereof and can simultaneously be applied to the adjacent one of the end surfaces as well as the side surfaces.
The process of the present invention can also be used to place a plurality of electrodes on a chip-like electronic part having a central axis, a polygonal cross section as viewed in a plane which is perpendicular to the central axis, a plurality of side surfaces extending in respective planes which are generally parallel to the central axis, and a pair of end surfaces extending generally parallel to the central axis, each adjacent pair of side surfaces meeting along a respective edge of the chip-like electronic part. In such a case, the process preferably comprising the steps of:
applying a set of first bands of conductive material to at least one of the side surfaces, each of the first bands being applied at a different axial position on the side surfaces so as to be spaced from one another; and
applying a set of second bands of conductive material to the remaining side surface(s), each of the second bands being applied at a different axial position of the remaining side surfaces so as to be spaced from one another, each band of the first set meeting a respective band of the first set at two respective edges such that each respective pair of bands forms a continuous band of conductive material extending around the outer periphery of the chip-type electronic part. More preferably, the chip-like electronic part has four side surfaces and is in the form of a quadrangular prism.
In the preferred embodiment, three continuous bands are formed, two adjacent the end surfaces of the chip-like electronic part, the third at a position intermediate the two end surfaces of the chip-like electronic part. The bands of conductive material are applied to the side surfaces by bringing them into contact with strips of conductive paste. In the preferred embodiment, the first applying step is carried out by holding the chip-type electronic part in a holder with the first and second side surfaces extending outwardly from the holder and the first set of bands are applied to the first and second side surfaces by moving a plurality of strips of conductive paste located on an elastic paste base into contact with the first and second side surfaces. Similarly, the second applying step is carried out by holding the chip-type electronic part in a holder with the third and fourth side surfaces extending outwardly from the holder and the second set of bands is applied to the third and fourth side surfaces by moving a plurality of strips of conductive paste located on an elastic paste base into contact with the third and fourth side surfaces. The same or different holders can be used for the first and second applying steps.
According to a further aspect of the process of the present invention, an electrode is formed on each of a plurality of chip-like electronic parts of the type having a central axis, a polygonal cross section as viewed in a plane which is perpendicular to the central axis, a plurality of side surfaces extending in respective planes which are generally parallel to the central axis, and a pair of end surfaces extending generally parallel to the central axis, each adjacent pair of side surfaces meeting along a respective edge of the chip-like electronic part, and the process comprises the steps of:
simultaneously applying a first band of conductive material to at least one of the side surfaces of each of the chip-like electronic parts; and
simultaneously applying a second band of conductive material to the remaining side surface(s) of each of the chip-like electronic parts in such a manner that the first and second bands of a respective chip-like electronic part meet at respective ones of the edges on that chip-like electronic part and together form a continuous band of conductive material extending around the outer periphery of that chip-type electronic part.
In the preferred embodiment, each of the chip-like electronic parts has four side surfaces and each of the first bands is applied to first and second contiguous side surfaces and wherein each of the second bands is applied to the remaining two side surfaces by bringing the side surfaces into contact with strips of conductive paste. The first applying step is carried out by holding each of the chip-type electronic parts in a single holder with the first and second side surfaces of each chip-like electronic part extending outwardly from the holder and the first band is applied to the first and second side surfaces of each of the chip-like electronic parts by moving respective strips of conductive paste located on an elastic paste base into contact with the first and second side surfaces. The second applying step is carried out by holding each of the chip-type electronic parts in a single holder with the third and fourth side surfaces extending outwardly from the holder and the second band is applied to the third and fourth side surfaces by moving strips of conductive paste located on an elastic paste base into contact with the third and fourth side surfaces. Again, a single or multiple holders can be used.
The present invention is also directed toward a combination, comprising:
a chip-like electronic part having a plurality of outer surfaces extending generally parallel to a central axis of the chip-like electronic part, at least one of the surfaces having a band of conductive material located thereon; and
a holder holding the chip-like conductive part in an orientation wherein at least one of the outer surfaces of the chip-like electronic part extends outwardly from the holder and wherein the surface(s) of the chip-like electronic part which have the band of conductive material located thereon face inwardly of the holder and are not exposed.
In the preferred embodiment, the holder includes a recess in which the band of conductive material is located without the conductive material touching the walls of the recess. The holder has a groove, including a plurality of side walls, for holding the electronic part, the shape of the groove corresponding generally to the shape of the portion of the chip-like electronic part being held in the groove. The walls of the chip-like electronic part which have the band of conductive material formed thereon are preferably in contact with the side walls of the groove and the band of conductive material itself is situated in a recess formed in the groove such that the band of conductive material does not contact the walls of the groove or the walls of the recess. When the chip-like electronic part is formed in a shape of a quadrangular prism, the groove is formed in a V-like shape.
The present invention is also directed towards a chip-like electronic part comprising:
a main body portion having a central axis, a polygonal cross section as viewed in a plane which is perpendicular to the central axis, a plurality of side surfaces extending in respective planes which are generally parallel to the central axis, and a pair of end surfaces extending generally parallel to the central axis, each adjacent pair of side surfaces meeting along a respective edge of the main body portion;
a pair of end electrodes located on the end surfaces of the main body portion; and
a central electrode comprising a sintered metal formed of an electrode paste and extending over each of the side surfaces of the main body portion so as to extend entirely around the outer periphery of the main body portion, the central electrode being formed of two bands of sintered conductive paste, the two bands meeting at respective edges of the main body portion.
The two respective edges are preferably located 180 degrees apart from one another as measured around the central axis of the main body portion with the two bands overlapping one another at the respective edges.